74 MORPHOLOGY AND EVOLUTION
confusion. There are, however, certain well-established species which can be recognized by their colour-markings, and possibly by the characters of their voices. ] »ablborn <,184) believed he could distinguish them by certain markings on the clavicles, but Keith (99) dissected several examples of each of a number of species and concluded that these had no taxonomic value.
In the Hainan Gibbon (H. hainanus), the face, palms, soles and ears are black, and there is no trace of a white circumfacial band. The hair on the body is soft, but devoid of woolliness. The head looks high, for the hairs on the vertex appear brushed upwards.
In all other species the hair on the crown is not porrect, and there is a varying degree of development of a white circumfacial band. In some species the hair on the wrists is grey or white. The circumfacial band is complete in the White-handed Gibbon (H. lar) from Burmah and the Malay Peninsula, the Slender Gibbon (H. agilis) from Malay and the Siamese Gibbon (H. irileatus). It is nearly complete in the Bornean Gibbon (H. Muelleri') and Silvery Gibbon (H. kitciscus). It is represented by a white supra-orbital strip in the Hoolock Gibbon (H. hoolock) from Further India; and it is reduced to a narrow submental strip in the White-cheeked Gibbon (H. leucogenys) of Siam. Sclater (209), Hermes (252),* Bishop (87) and Pocock (223) have published illustrations showing the external characters of some of the above mentioned species.*
* Accounts of external characters of Gibbons are given in papers
176, 178, 179, 182, l83» 190, 198, Ipp, 200, 201, 203, 204, 207, 209, 210, 211*216, 220, 223.